Characterization and Overexpression of a Glucosyltransferase Gene from Streptococcus mutans

Bian/Fan/Li/Du/He

Objective: Streptococcus mutans produces 3 distinct glucosyltransferases (Gtase): Gtase-1, Gtase-SI, and Gtase-S. These enzymes synthesize from sucrose water-soluble and insoluble glucan that act cooperatively in mediating S. mutans adherence to tooth surface and dental plaque formation. This study investigated the relationship between the sucrose-dependent adherence and Gtase-1 expression level. Methods: In this study a Streptococcus-Escherichia coli shutter vector carrying Gtase-I gene, pZB1, was constructed. The gene pZBI was then transformed into S. mutans Gtase-I-deficient mutant B29. Two types of Gtase-1 expressing strain were obtained: Gtase-I expression strain similar to the parent and a GTase-I overexpression strain. Results: Sucrose-dependent adherence of these mutants was closely related to the amount of initial bacterial inoculum in the experiment, that is a msall inoculum resulted in firm adherence and vice versa. The plasmid was reisolated from the Gtase-I overexpressing strain. Nucleotide sequencing revealed that no mutation was found upstream of the Gtase-I gene when compared with pZB1. Conclusion: The balance in the quantity of Gtase-I and Gtase-SI may play an important role in the adherence of S. mutans in the presence of sucrose.